基于K_0固结排水卸荷应力路径试验粉土应力–变形特性研究

Stress-deformation characteristics of silty soil based on K_0 consolidation and drainage unloading stress path tests

针对开挖土体复杂卸荷应力路径,按不同初始应力状态和卸荷应力比,对南水北调南干渠粉质黏土开展了K_0固结排水卸荷应力路径试验。试样首先在不同围压条件下K_0固结稳定,然后根据不同的轴向应力和径向应力卸荷比,进行卸荷试验,以模拟实际土体开挖过程中的应力路径。试验结果表明土体的应力应变特性与应力路径密切相关:不同卸荷应力比条件下,试样可能为压缩,先伸长再压缩或者为伸长变形;卸荷应力路径下压缩和伸长应力比临界值与初始固结状态和土性相关;相同平均应力增量条件下,卸荷应力比越小,试样体积膨胀绝对值越大;土体强度参数受加荷方式和应力路径影响不大。试验结果和常规三轴试验有显著区别,需要发展能够描述卸荷应力路径下的土体本构模型,对开挖土体开展符合工程实际的应力变形分析。

Based on different initial stress states and unloading stress ratios, the unloading stress path drainage tests under K0 consolidation are carried out on the silty clay sampled from the construction site of the South-to-North Water Diversion Project. The specimens are firstly consolidated with a given value of K0 under different confining pressures. Then, to simulate the stress path at different locations of excavatiorr soil, the stress decrements are applied from both the axial and the radial directions with different stress ratios. The test results show that the stress-strain behavior of soil is closely related to the stress path. Under different unloading stress ratios, the specimen may be compressed, elongated firstly and then compressed or elongated. The critical value of unloading stress ratio determining compression and extension is determined by the initial consolidation state and soil properties. With the decrement of the unloading stress ratio, the value of volume dilation increases. The tests also verify that the loading mode and stress path have little effect on the strength parameters. The characteristics observed from the tests are significantly different from those of the conventional triaxial test results. It is necessary to develop a proper constitutive model, which can describe the unloading stress path of the soil, and to carry out the stress and deformation analysis of the excavation soil.